The University Record, May 22, 1995
Skywatchers who glance at the rising or setting sun are sometimes surprised to see sunspots. Although there is no way to predict with certainty when such sunspots might be visible to the naked eye, chances are good that they may appear sometime within the next 12 months, according to astronomer Richard Teske.
If you look for sunspots, Teske warns that you should do so only at sunrise or sunset, or when the sun is almost hidden behind a veil of fog or clouds, so its scorching light will not harm your eyes.
Scientists who use telescopes to study the sun have known that dark spots frequently appear on its surface. The spots are cooler regions in the sun's outer layers that shine less brilliantly than the rest of its surface. "Sunspots are regions of powerful magnetism, which has the effect of lowering the normal 9,900 F temperature of the sun's visible layers to 'only' 7,900 F," Teske says.
Sunspots become visible when magnetic fields from deep within the sun penetrate through its gaseous outer layers, according to Teske. The spots are born in groups that usually have fewer than a dozen members, although occasionally a sunspot group may be made up of 100 or more. The members of a group are constantly shifting about, appearing and disappearing. A single small member lives one or two days, while a typical group lasts a week or more.
"Even though some of the individual spots are as large as the Earth or even larger, a telescope is usually needed to see them across the 93 million miles between Earth and sun," Teske says. "Only rarely do spots appear that are so immense they can be seen without optical help. But it's possible some may become visible in 1995 or the first half of 1996. Their size dwarfs even the largest planet, Jupiter."
There is an increased chance of seeing a naked eye sunspot during the next year or two because of the way their occurrence is connected to the sun's 11-year sunspot cycle, Teske explains. "During some years of the cycle, many spot groups are seen coming and going on the sun, while in other years sunspot groups are almost absent. The greatest number recently recorded was in mid-1989. Since then the number of sunspot groups logged by solar astronomers has been diminishing year by year," Teske says.
"Right now the sun is approaching a time of minimum spottedness, expected early in 1997. After 1997, the number of sunspots will increase again. But now, as sunspot minimum approaches, the likelihood of catching sight of a naked eye sunspot improves." For some unknown reason, according to Teske, naked eye sunspots are more likely to appear during the last few years before one sunspot cycle ends and the next begins.
If you track a naked eye sunspot as it appears every day at sunrise or sunset, you can see the sun rotating on its axis, according to Teske. "Observers who want to try this will see the sunspot gradually change its position against the sun's face, marking the sun's spin. They will find that, at sunrise, the part of the sun that first peeps over the horizon is the side that is rotating away from us. At sunset, the last part of the sun to sink out of sight is coming toward the Earth."
Our sun's spin is slow by the standards of some other stars. Its 2.6-million-mile circumference rotates once every 27 days, as seen from Earth. Sunspot groups that live for a month or more are carried around to the invisible back side of the sun by its ponderous rotation, and disappear from our view for two weeks, Teske explains. Later they come into sight once again on the side of the sun opposite from where they disappeared from Earth's view.